"Passive" restraint apparatus, which requires no action by a vehicle occupant to render operative, as contrasted to "active" restraint apparatus requiring a conscious effort by an occupant to render operative (such as conventional seat belts), are now commonly included as standard equipment in motor vehicles due to government agency, insurance industry, and consumer pressures. Experience and testing have shown that the most effective passive occupant restraint approach is to abruptly (in a matter of milliseconds) inflate an airbag automatically in response to a high impact accident. The inflated air bag cushions a vehicle occupant from the effects of the accident for an interval sufficient to prevent serious injury.
The typical airbag inflation apparatus uses ignitable propellants that are combusted to rapidly generating a large volume of bag inflation gas by exothermic reaction. Heretofore, the propellants invariably have been in a solid or granular form and comprised of low energy compositions, such as an alkali metal azide, cupric oxide, boron nitrate, etc. The solid propellants need not be stored under pressure, are stable over time under varying ambient conditions, and are convenient to package in a passive restraint apparatus.
As an alternative to the use of propellants in solid or granular form as the inflation gas generator, liquid propellants for this purpose are being investigated. Viable approaches to using a liquid propellant in an airbag inflator are disclosed in U.S. Pat. No. 5,060,973, issued to Giovanetti; U.S. Pat. Nos. 5,487,561 and 5,639,117, issued to Mandzy et al.; and Messina et al., U.S. patent application Ser. No. 08/674,063, filed Jul. 1, 1996. The numerous advantages afforded by the use of liquid propellants in an airbag inflation apparatus are noted in these patent documents, the disclosures of which are incorporated herein by reference.
To protect passengers, as well as drivers of vehicles, airbags are now being installed in dashboards for protection against frontal collisions and in doors for protection against side impact collisions. Bag size and inflation parameters are dependent on the particular installation site, and each installation varies according to vehicle type and make. Thus, bag inflators must be designed not only to satisfy the unique inflation parameters appropriate for each particular installation site, but also must be sized to fit into the available space that is unique to each installation site. Regarding inflation parameters, recent studies have indicated that particularly abrupt bag inflation, rather than protecting vehicle occupants in the event of a high impact accident, may instead inflict injury, even death, to occupants; this is particularly so in the case of children.